The continued study of early interactions of rabies virus for cell surface receptors will focus on the chemical nature of the cellular receptor on cultured cells and the development of probes of this receptor to study the relevance of in vitro findings to the attachment of rabies virus in vivo. Our previous studies suggested that rabies virus attaches to a cell surface component which may be lipid in nature. Thus, we will investigate rabies virus attachment to various structurally characterized glycolipids of animal origin. We will determine the biologic specificity of virus-glycolipid interactions using liposomes containing the various glycolipids in attachment and infectivity inhibition assays. The pH dependent cell-cell fusion in cultures of rabies virus-infected cells will be studied by investigating acid-induced conformational change in the rabies virus glycoprotein. Monoclonal antibodies directed toward the viral glycoprotein will locate regions of conformational change by comparative antigenic analysis. Also, acid-treated viral glycoprotein will be compared to untreated glycoprotein for the specificity of binding to neutral glycolipids suggesting a 'second binding site' of the virus glycoprotein related to adsorptive endocytosis. We will continue to develop soluble receptor probes for use in vivo. These will include anti-idiotypic antibodies, representing conformational images of individual glycoprotein epitopes, and radiolabeled virus to observe virus distribution in cryostat sections of various tissues. We will determine the relationship between rabies virus and isolated acetylcholine receptor in direct binding and binding competition assays using a panel of monoclonal antibodies directed against the acetylcholine receptor complex. Finally, we will attempt to localize discrete areas on the rabies virus glycoprotein responsible for attachment and fusion by using monovalent (Fab) fragments of anti-glycoprotein monoclonal antibodies. These studies are aimed at understanding the nature of viral tropism using the struct neurotropic pathogen, rabies virus, as a model.